Known automation or control systems for controlling a technical process or a technical installation can include a central or superordinate unit, for example a programmable logic controller (PLC) or a process control system (PCS). The central control unit communicates with the field devices of the automation system via a communication interface module (also called gateway device). In this case, the gateway device makes it possible for field buses of different protocols to communicate. For communication between field bus systems which process different protocols, the gateway device communicates with the central control unit using a Profinet protocol, for example, and communicates with input/output devices and/or field devices connected thereto via a field bus protocol, for example CAN or CANopen.
Different field devices can be used to record and/or influence process variables which are, for example, current measured values provided by sensors. The recorded current measured values are transmitted according to the prior art in the form of so-called process data objects from the field level to the gateway device using a field bus protocol having a low transmission rate of 1.2 Kbit/s, for example, and are forwarded from the gateway device to the superordinate control unit via a high-speed Ethernet bus. The process data objects are used to transport real-time data.
Process control is usually effected by the control unit, where the measured values from different field devices are evaluated and control signals for actuators connected to the automation system are generated based on the evaluation. In addition to purely transmitting measured values, field devices may also transmit additional information, such as diagnostic and status information, to the superordinate control unit. The field devices are likewise parameterized and configured via the bus system or network of the control or automation system. In this case, signals can be transmitted between the field device and the control unit in analog or digital form as binary code (Boolean value) or an integer value.
In gateway devices, according to the prior art, the process map of the installation, which was transmitted in the form of process data objects to the gateway device using a secondary field bus protocol with a low transmission rate, is first of all mapped as a secondary network variable in binary format in the gateway device and is converted into a primary network variable which is in byte format and can then be transmitted to the superordinate control unit using the primary high-speed Ethernet bus protocol.
However, this method specifies a wide bandwidth and burdens the data traffic on the primary high-speed Ethernet bus since seven bits of overhead should be provided for each bit, in which case overhead should be understood as meaning data which do not primarily belong to the useful data but rather are specified as additional information for transmission or storage.
A CANopen communication protocol may transmit, for example, only 1028 binary signals corresponding to approximately 130 bytes (=128.5 bytes), which limits the upper limit of the process data size for a device connected to the Profinet bus to 1028 bytes. The number of items of information which can be transmitted is therefore restricted by the limited message size which can be transmitted using the primary network protocol.